Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis.

We examined the melt and solid-state structures of a series of diblock copolymers containing polyethylene as the minority block, with a rubbery hydrocarbon majority block. When the interblock segregation strength during crystallization is sufficiently high (approximately 3 times the segregation strength at the order−disorder transition), crystallization can be effectively confined within spherical domains formed by microphase separation in the melt; the process is homogeneously nucleated, and the resulting kinetics are first-order (Avrami n = 1). Below this critical interblock segregation strength, crystallization disrupts the spherical microdomains, resulting in sigmoidal kinetics (n > 1). Cylinder-forming materials are more complex:  there exists a range of intermediate segregation strength where crystallization is templated but not wholly confined within the nanoscale domains prescribed by microphase separation; while the melt morphology is generally retained on cooling, local distortions and connections between cylinders occur due to crystallization. These intercylinder connections allow the material initially contained within several cylinders to be crystallized by a single nucleus, producing sigmoidal kinetics and a dramatic acceleration of the overall crystallization rate, despite the general preservation of the cylindrical structure.

The appeal of organic electronics stems from the promise of low-cost and disposable device applications. These applications tend to focus on macroelectronics in the arenas of largearea displays, electronic bar codes and identification tags, and flexible electronics, such as wearable sensors, electronic paper, and so forth. [1][2][3] To fully realize the low-cost aspects of organic electronics, existing [4,5] and emerging [6][7][8] vacuum-processing techniques to create devices will have to be replaced by solution-processing technologies that are lower in capital and operation costs, such as spin-coating and inkjet printing. [3,[9][10][11][12][13] This goal has in turn driven the need for solutionprocessable organic conductors and semiconductors. Recently, research in this area has focused on the development of air, moisture, and light-stable, solution-processable organic semiconductors [1,5,14] given that previous-generation materials have been very sensitive to their environment. [2,15] These new, solution-processable organic semiconductors [16][17][18][19][20] are typically semicrystalline polymers [16,[21][22][23] or small-molecule organic precursors that require subsequent chemical and/or thermal conversion after deposition [17,[24][25][26] to become electrically active. While these materials can be easily deposited by means of inkjet printing or spin-coating, the details of the processing conditions frequently dictate the final film structure and morphology (e.g., crystallinity, grain size, molecular orientation, etc.), [21,27,28] which in turn affect their macroscopic electrical properties. [17,26,29] The resulting devices therefore tend to exhibit characteristics that are significantly poorer than devices made with thermally evaporated organic semiconductors. Since molecular ordering is believed to play an important role in determining the performance of organic devices, [30][31][32] there exists a critical need for simple methods to increase crystallinity and enhance grain growth in as-deposited, solution-processable organic semiconductors. In this communication, we report on how a straightforward, one-step, solventvapor-annealing process [33] can dramatically improve the electrical properties of a solution-processable, p-type organic semiconductor, triethylsilylethynyl anthradithiophene (TES ADT, see Scheme 1). [19,34] To evaluate its electrical properties, we built and tested bottom-contact thin-film transistors (TFTs) on silicon, on which TES ADT was directly spin-coated. The subsequent solvent-vapor annealing is a physical process that enhances grain growth and thin-film crystallinity of the spin-coated TES ADT; additional reactions-either by thermal or chemical means-to convert the as-deposited material into an electrically active organic semiconductor are not necessary. A recent publication on TES ADT has demonstrated its solution processability and chemical stability. [19] While TFTs built with this material can exhibit high saturation mobility, the statistics vary significantly and appear to corre...

We report an efficiency of 6.1% for a solution-processed non-fullerene solar cell using a helical perylene diimide (PDI) dimer as the electron acceptor. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor-acceptor interfaces, indicating that charge carriers are created from photogenerated excitons in both the electron donor and acceptor phases. Light-intensity-dependent current-voltage measurements suggested different recombination rates under short-circuit and open-circuit conditions.

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor−acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells.

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Directing efficient hole transport Surface defects in three-dimensional perovskites can decrease performance but can be healed with coatings based on two-dimensional (2D) perovskite such as Ruddlesden-Popper phases. However, the bulky organic groups of these 2D phases can lead to low and anisotropic charge transport. F. Zhang et al . show that a metastable polymorph of a Dion-Jacobson 2D structure based on asymmetric organic molecules reduced the energy barrier for hole transport and their transport through the layer. When used as a top layer for a triple-cation mixed-halide perovskite, a solar cell retained 90% of its initial power conversion efficiency of 24.7% after 1000 hours of operation at approximately 40°C in nitrogen. —PDS

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